Field of the Invention
The present invention relates to a technique of measuring an optical characteristic of a surface.
Description of the Related Art
The optical characteristic of the surface of an object such as a printed product, a coating, or a plastic material is an important factor associated with quality. As methods of measuring the optical characteristic of an object surface, there exist methods of measuring, for example, a specular gloss, a DOI (Distinct Of Image), Haze, and the like. In a conventional optical characteristic measuring apparatus, incident light is focused to a predetermined angle of aperture, a surface is irradiated at a predetermined angle of incidence, and reflected light from the surface is focused to a predetermined angle of aperture and received by a light receiving element such as a PD (photodiode) or a line sensor, thereby performing measurement. Japanese Patent Laid-Open No. 2007-225384 discloses a method that removes a stop on the light receiving side and uses a two-dimensional area sensor as a light receiving element, thereby enabling measurement even in a case in which the surface tilts, and the light receiving range moves.
In the technique of Japanese Patent Laid-Open No. 2007-225384, it is necessary to use an area sensor having a wide region enough to cover the irradiation region of reflected light. Since the recent mainstream is a megapixel sensor that includes at least several million pixels and attains a high resolution, an enormous amount of data is needed to acquire reflected light in a wide region. For this reason, the amount of calculation necessary for measurement processing increases, and data transfer takes time. A CPU capable of high-speed processing and a mass memory are needed, resulting in an increase in cost. In Japanese Patent Laid-Open No. 2007-225384, mention is made of only measurement at a single angle. If the apparatus is configured to measure at a plurality of angles, the problem becomes more conspicuous.